1. Field of the Invention
This invention relates to a method and apparatus for multiplying a frequency of an input electromagnetic wave and, in particular, to such a method and an apparatus that are usable for microwave and high frequency fields, which often require the frequency multiplication in a mobile communication device or a cellular information instrument.
2. Description of the Prior Art
A frequency generated at and transmitted from a mobile communication device or a cellular information instrument can be multiplied by taking advantage of the non-linear resistance performance of a crystal detector. In this case, however, since many elements must be controlled and matched, the operation becomes complicated.
On the other hand, a monolithic microwave integrated circuit can be employed in which a given microwave circuit is fabricated, as a high speed and high frequency circuit, on a single substrate. Since it can be reliably mass produced, the monolithic microwave integrated circuit is preferably employed for commercial use. However, it is desired that the monolithic integrated circuit operate at a higher frequency, be of low cost, be susceptible to miniaturization and weight reduction, and consumer low amounts of electric power.
It is an object of the present invention to provide a new method for multiplying a frequency and an instrument for implementing the method.
For achieving the above object, this invention relates to a method for multiplying a frequency, comprising the steps of providing a ferromagnetic film, which has an inherent resonant frequency, and introducing an electromagnetic wave, which has an input frequency equal to the resonant frequency of the ferromagnetic film. Introducing the electromagnetic wave generates a ferromagnetic resonance in the ferromagnetic film and thus, multiplies the input frequency of the introduced electromagnetic wave.
The present invention takes advantage of the ferromagnetic resonance of a ferromagnetic film, as described further below.
FIG. 1 is a diagram that is useful for explaining the principles according to the present invention. In the ferromagnetic resonance of a ferromagnetic film, the magnetic moment M is affected by a diamagnetic field, which is generated in the direction perpendicular to the main surface of a ferromagnetic film. Thus the magnetic moment M has a large amplitude in the direction parallel to the main surface and a small amplitude in the direction perpendicular to the main surface. In this case, the magnetic moment M oscillates twice in a Z direction while oscillating once in a X direction, as shown in FIG. 1. Therefore, if a ferromagnetic resonance is generated at a resonant frequency of f, the magnetic moment M oscillates f times in the X direction and 2f times in the Z direction.
If an electromagnetic wave having almost the same input frequency as the resonant frequency f is introduced into the ferromagnetic film, a ferromagnetic resonance is generated as described above. As explained above, the magnetic moment M oscillates in a frequency of 2f in the Z direction and radiates an electromagnetic wave having a frequency of 2f. As a result, the input frequency of the introduced electromagnetic wave doubled. The frequency of a given electromagnetic wave can be multiplied by using the ferromagnetic resonance of a ferromagnetic film.
The resonant frequency of a ferromagnetic film can be adjusted as appropriate for a particular use by appropriately adjusting the type of the ferromagnetic material, the thickness, and other properties of the film. Therefore, the present invention can effectively multiply the input frequency of an electromagnetic wave for a wide range of input frequencies.
Also, since the dimensions of the ferromagnetic film are in the order of nanometers, the present invention can be miniaturized. Because the ferromagnetic resonance is generated without an external magnetic field, excess electric power is not consumed to generate the magnetic field, resulting in lower power consumption.
In addition, the ferromagnetic film may be made of a Co single crystal film, as discussed below, which is not expensive, and the present invention does not require an additional external magnet. Therefore, the multiplying method and apparatus of the present invention can be inexpensive.